An engine failure that was a new one on me

[jracer98]

At the end of last season, an engine I had built (alcohol 4 bbl 358 SBC, pavement mod, top components) that had run well for about 15 nights since I freshed it, started to "tighten up" in a race. The driver shut it down before it blew up(way to go, Marc). I got it apart over the winter and the center 4 rod bearings were oil starved. Cleaned it all up, turned the crank, put in 4 new rods (overkill) and got it back together. I looked over the oiling system closely but nothing jumped out at me. Replaced the oiling system with the new style Melling with the big bolt on pick up.

Put it in the car today and spun up oil pressure (60psi) with the pre luber. In goes the distributor (Performance HEI). Started it up and ZERO pressure. I know it's in the drive somewhere because I just had OP with the pre luber and drill motor.

 

The damn drive tang was gone of the bottom of the distributor shaft, up inside the cam drive gear. Put in a new shaft and all was well. Going forward I intend to magnaflux that shaft every rebuild ... and so should you.

Trust me on this.

 

Jay

Edited April 10, 2007 by jracer98

[racer61]

thanks. Checked out one of my old msd dist.s out of the last disaster, yep gear is bad. Never take anything for granted.

[xcellracing]

....or quit buying cheap gears made of soft metal

[jracer98]

Just to be clearer, the drive tang that broke off inserts into the oil pump drive shaft and is cut into the distributor's steel shaft. The distributor gear fits over this shaft and is secured by a roll pin. The distributor gear was not a part of the problem.

Just trying to help others.

Jay

[zoom]

Thats new one to me. Thanks I will watch that part as well. One question, what oil pump were you running when it broke off? Didn't you find the pieces in the pan or did it snap off and stay in the cavity created by the cam gear?

[jracer98]

Melling 55 SBC std/std (the older style with the "push in" pickup that also attaches to the bottom cover bolt.

Good pan, the right pickup, Valvoline 20/50 Racing.

I did not notice the drive tang was broken off when the distributor came out of the hurt engine. Like most folks, I pull the intake and heads and then flip it over to start on the bottom end. I assume the tang "fell" down into the short block at that point. I did not see it at the time as I was all over the hurt rods and rod throws of the crank. Said another way, it was probably up in the shortblock at that point but I wasn't "looking for it" so to speak. The broken off part would look sort of like a crank key that was about 3/8 inch long.

 

It was just a fluke and I wanted to tell the story because it would be easy to take the shaft out and the gear off at rebuild time and have it zyglo'd/magnafluxed with the rest of the stuff.

Marc being heads up enough to shut it down cut the potential bill in half but it's $1500 in parts and machine work.

Just wanted to make engine folks aware.

Jay

Edited April 11, 2007 by jracer98

[xcellracing]

Yeah your right not the gear, but maybe cutting heads intake and stuff, you also need to make sure the distributor is meshing properly with the cam gear and that your end play is not to much that it forces the dist. gear up and barely catching the tang and on the dyno 20/50 oil cost me 3hp over straight 30 not to mention the strain on the dist tang going from 80-85 psi down to 65psi on the pressure. although sounds like a fluke thing or just plain old wore out parts thats not something you have on a checklist normally.Also coulda been an oilpump failure that locked up and broke the shaft also. Did you pull the pump apart? you were difinatly lucky your not starting over with a block with no holes

[jracer98]

I wondered if the original OP has eaten some debris, locked up and therefore the distributor drive tang was the weak link that failed first but when I got the OP off the shortblock, it spun by hand and felt normal. I didn't actually take it apart as it was headed for the trash.

 

It a chicken/egg thing. There wasn't any debris until the dist. shaft failed and the small amount of junk came "afterwards" from the degenerated bearings.

 

That block did not measure unusually in any way and was not even decked to 9. I am careful about the installed height the distributor. The engine has an 2 part timing cover that has thick pieces (not stamped) and an adjustable length button for the roller.

 

I'm writing it off to bad luck and just throwing up an FYI to others.

 

Jay

[zoom]

And thank you for the info.

I am adding it to the memory bank. But I had better put it in a journal since the memory bank is pretty dusty.

 

thanks again

[lbeaver087]

if you bought the mellings oil pump like bought for my new motor it was a high volume pump , if you read the paper work in the box it says to but a new shaft with a steel sleeve.

[xcellracing]

J, if it werent for bad luck i would have no luck at all